> Why would it not be possible to fashion an extremely powerful laser and sweep it across the sky in an area where gravitational clues indicate a dark object may reside?
Lasers are not the important part here- collimation is. The closer the illumination is to a perfect cylinder, the more visible it stays. Lasers often happen to be highly collimated, but it's not a defining feature. For instance laser diodes emit laser light in a cone 20+ degrees wide, and lenses are needed to produce a beam.
Bottom line: lasers aren't a panacea- generating a collimated beam isn't trivial, and just because we can make immensely powerful lasers that doesn't mean they are collimated.
> Unless the object was utterly black on its surface, I'd think we would be able to monitor wherever the beam traverses and look for tell-tale spectra coming back in our direction due to the laser being scattered by a solid object's surface.
There isn't really any tell-tale spectrum available- obviously you need something below X-rays, because those will be absorbed rather than reflected. In practice you also need something above millimeter waves, because those are also absorbed but more importantly the collimation of an EM source is inversely proportional to its wavelength. So millimeter waves are ~2000x less collimated than visible light, unless you use a massive antenna.
Just above millimeter waves are infrared waves, and just below X-rays are ultraviolet waves. Along that entire range, the sun is very active, so any light is going to be washed out against that background. You don't really get to rely on the spectra being unique.
> the necessary power needed for a laser strong enough to travel to such a distant point (it might not be physically possible to create a laser large enough to exceed the light we would already see reflected back from the already formidable output of the Sun)
The reflected light of the laser has to be brighter than the suns reflection over the entire area of the object you're trying to see. For an Earth-sized object at 1000 AU, that's 174 gigawatts. Not only do you have the impossible task of actually hitting the object, you need to have a hundred nuclear reactors powering a single source the entire time you do it.
Not to say this is in any way practical, but lasers used for nuclear fusion research are up in the petawatt range. They've just got extremely short pulses. But if all you need to do is detect that pulse coming back, like a radar return, it starts to sound within the range of conceivable engineering, not a total physical impossibility.
Lasers are not the important part here- collimation is. The closer the illumination is to a perfect cylinder, the more visible it stays. Lasers often happen to be highly collimated, but it's not a defining feature. For instance laser diodes emit laser light in a cone 20+ degrees wide, and lenses are needed to produce a beam.
Bottom line: lasers aren't a panacea- generating a collimated beam isn't trivial, and just because we can make immensely powerful lasers that doesn't mean they are collimated.
> Unless the object was utterly black on its surface, I'd think we would be able to monitor wherever the beam traverses and look for tell-tale spectra coming back in our direction due to the laser being scattered by a solid object's surface.
There isn't really any tell-tale spectrum available- obviously you need something below X-rays, because those will be absorbed rather than reflected. In practice you also need something above millimeter waves, because those are also absorbed but more importantly the collimation of an EM source is inversely proportional to its wavelength. So millimeter waves are ~2000x less collimated than visible light, unless you use a massive antenna.
Just above millimeter waves are infrared waves, and just below X-rays are ultraviolet waves. Along that entire range, the sun is very active, so any light is going to be washed out against that background. You don't really get to rely on the spectra being unique.
> the necessary power needed for a laser strong enough to travel to such a distant point (it might not be physically possible to create a laser large enough to exceed the light we would already see reflected back from the already formidable output of the Sun)
The reflected light of the laser has to be brighter than the suns reflection over the entire area of the object you're trying to see. For an Earth-sized object at 1000 AU, that's 174 gigawatts. Not only do you have the impossible task of actually hitting the object, you need to have a hundred nuclear reactors powering a single source the entire time you do it.